It is suppose to be a chuppa, not a tallis. A Tallis is only used as a make-shift chuppa, and is always to hand in shul, unlike a real chuppa, which may not be large enough for all the children (also, there is no reason for adults to be there – they all already got an aliya earlier). So, this is really just a very large chuppa canopy, without the legs & frame, that is designed to look like a tallis. No one is going to , or can actually wear this chuppa, so there is no need to put tzitzis on it, and possibly even wrong to put tzizis on it.